1. Field of the Invention
The present invention relates generally to machines used to separate particulate materials or mixed recyclable materials into difference fractions, and more particularly, to a disc construction for a disc screen that allows its discs to be more easily removed and replaced.
2. Related Art
Disc screens have long been used to separate particulate materials such as wood chips into difference fractions, according to size. More recently disc screens have been used to separate or classify mixed recyclable materials into respective streams of similar materials such as broken glass, containers, mixed paper and newspaper.
A disc screen typically includes a frame in which a plurality of rotatable shafts are mounted in parallel relationship. A plurality of discs are mounted on each shaft and a chain drive rotates the shafts in the same direction. The discs on one shaft interleave with the discs on each adjacent shaft to form screen openings between the peripheral edges of the discs. The size of the openings determines the dimension (and thus the type) of material that will fall through the screen. Rotation of the discs, which have an irregular outer contour, agitates the mixed recyclable materials to enhance classification. The rotating discs also propel the larger articles which are too big to fall between the discs across the screen. The general flow direction extends from an input area where the stream of material pours onto the disc screen to an output where the larger articles pour off of the disc screen. The smaller articles fall between the discs onto another disc screen or a conveyor, or into a collection bin.
The discs of a disc screen normally have a central opening or bore that allows them to be slid over the end of a shaft which may have a round or square cross-section. See for example U.S. Pat. No. 4,836,388 of Bielagus granted Jun. 6, 1989. Over time, the discs wear out and must be replaced. It is not practical to re-surface or repair damaged or worn discs without removing them from the shafts of the disc screen. However, it is tedious to dismount the ends of the shafts of a disc screen from their respective bearings so that the old discs can be removed and replaced by sliding the discs off the ends of the shafts. Moreover, if only singe disc is worn out or broken, it is usually necessary to remove several discs before the damaged or broken disc can be slid off the shaft. In order to alleviate these problems, a split disc was developed by CP Manufacturing, Inc. of National City, Calif. See U.S. Pat. No. 6,318,560 of Robert M. Davis granted Nov. 20, 2001. The split disc is comprised of two identical halves which are assembled around a shaft and tightly held together by a pair of bolt assemblies which clamp the disc to the shaft. Each disc half is made of an outer rubber portion which is stiffened with a rigid internal metal frame embedded inside the rubber portion. While the aforementioned patented two-piece disc construction has been commercially successful, it would be desirable to provide a disc construction that is even more convenient to remove and install.